1. Field of the Invention
The invention relates to machine tool control systems.
2. Description of the Related Art
In recent years, many forms of machine tool including computer numerical control (CNC) systems have been developed. In such machine tools, a workpiece is rotated and a tool moved in two mutually perpendicular directions by stepping motors controlled to produce a required workpiece profile from data defining the required profile and held in digital form in a control system. In such CNC machine tools, however, the motor which rotates the workpiece is not controlled by the control unit; rather it is rotated independently and a workpiece position transducer is used to feed to the control system a signal corresponding to the angular position of the workpiece.
It is a disadvantage of such CNC systems that they have to perform a feedback function to account for variations in the speed of workpiece drive. This has the disadvantage that valuable data storage space and computing time are taken in performing this function, so reducing the overall machining speed.